JPH1177376A - Flux - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the residue which generates no cracks and is flexible even under severe change in temperature by containing fatty acid ester of polyglycerin in the soldering flux. SOLUTION: The soldering flux consists of rosin resin such as rubber rosin, hydrogenated rosin, polymerized resin and modified resin as a basic material. The flux contains halide hydroacid salt and organic acid. The flux contains diethylene-glycol monohexyl-ether, diethylene-glycol-dibutyl-ether, α-terpineol as the solvent. The content of fatty acid ester in polyglycerin is preferably 0.1-30% of the whole flux, and more preferably, 0.5-20%. The flux is well mixed with solder powder to obtain the cream solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux mainly used for mounting an electronic component or the like on a printed circuit board and a cream solder containing the flux.

[0002]

2. Description of the Related Art Fluxes and cream solders used for soldering for mounting electronic components and the like on printed circuit boards have been required to have new performance corresponding to the progress of mounting technology. In particular, the tendency is strong in a cream solder in which a flux and a solder powder are mixed.
The flux for soldering is composed of components such as a rosin resin, an activator, and a solvent. In addition, it is general that a flux for cream solder further contains a thixotropic agent in order to further improve printing characteristics. After soldering the electronic components to the printed circuit board, some of those components remain on the printed circuit board. This is called flux residue. The flux residue has been washed and removed with a solvent such as chlorofluorocarbon from the viewpoint of the electrical reliability of the printed circuit board. That is, a non-cleaning type has been required. Therefore, even if there is a residue on the printed circuit board, it is necessary to ensure electrical reliability. In other words, the electrical reliability of the flux residue is important. Further, electrical reliability under high temperature and high humidity is also required. Furthermore, it is necessary to withstand a severe temperature change of the environment atmosphere where the printed circuit board is placed, that is, a thermal shock, and to maintain its electrical reliability.

[0003] However, conventional fluxes and flux residues from cream solder cannot cope with such temperature changes and are liable to cracks. When a crack occurs, moisture in the air penetrates from the crack, migration occurs, and electrical reliability is significantly reduced.
Further, since the residue is brittle and inflexible, the residue is broken at the time of pin contact in the in-circuit test, and the fragments adhere to the needle tip of the tester, so that the test cannot be performed smoothly. Furthermore, since it has no flexibility, it has been difficult to use it for a flexible electronic substrate.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the conventional flux and cream solder. In other words, an object of the present invention is to provide a flux and a cream solder which do not crack even under a severe temperature change and provide a flexible residue while maintaining electrical reliability.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above-mentioned object, and as a result, it has been found that the object can be achieved by adding a fatty acid ester of polyglycerin to the flux. And arrived at the present invention. That is, the first of the present invention is a soldering flux containing a fatty acid ester of polyglycerin, and the second is a cream containing this flux and a solder powder.

The fatty acid ester of polyglycerin used in the present invention is usually produced by the following method. (1) Ester reaction between polyglycerin and fatty acid (2) Ester exchange reaction between polyglycerin and fat (3) Ester exchange reaction between polyglycerin and fatty acid methyl or ethyl ester (4) Addition polymerization reaction of glycidol to fatty acid

[0007] Here, polyglycerin is a high-viscosity liquid obtained by heating and dehydrating and condensing glycerin in the presence of a catalyst. The degree of polymerization differs depending on the conditions of the condensation reaction. The approximate degree of polymerization is determined from the measured hydroxyl value. Depending on the degree of polymerization, they are called diglycerin, triglycerin, tetraglycerin, pentaglycerin, hexaglycerin, heptaglycerin, octaglycerin, and the like. In practice, mixtures thereof are treated as industrial products. Such polyglycerin is converted into an ester by reaction with a fatty acid as described above. Fatty acids include stearic acid, oleic acid, ricinoleic acid, lauric acid, caprylic acid, condensed ricinoleic acid, and the like. Since polyglycerin is a polyhydric alcohol, it becomes various esters such as mono-, tri-, penta- and hepta, depending on the molar ratio with the fatty acid. Oleic esters are liquid at room temperature, while stearic esters are mostly solid. These are dispersed in water and have surface activity. For example, it is a flaky solid such as decaglycerin monostearate, decaglycerin decastearate, hexaglycerin pentastearate, and tetraglycerin stearate. Also, decaglycerin sesquioleate,
Hexaglycerin oleate pentaester, decaglycerin laurate monoester, tetraglycerin laurate monoester, decaglycerin caprylic acid monoester, polyglycerin condensed ricinoleate, and the like are liquids.

[0008] In general, the flux for soldering uses a rosin-based resin such as gum rosin, hydrogenated rosin, polymerized rosin, modified rosin or the like as a base material, and further uses an amine hydrohalide or an organic acid as an activator. , Diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, α-terpineol, etc. as solvents. If necessary, the composition may further contain a hydrogenated castor oil or a higher fatty acid amide as a thixotropic agent, or may contain a stabilizer or the like. Usually, the flux for cream solder is a viscous liquid or paste.

The rosin resin has a softening point of 70 to 150 ° C.
If the flux base of the cream solder is such a rosin-based resin, the residue after soldering is also brittle, especially at low temperatures of 0 ° C or lower, due to the difference in heat shrinkage with the printed circuit board. Can not be absorbed, and cracks are generated, and moisture in the air enters there, thereby impairing electrical reliability.

[0010] The present invention is characterized in that a flux comprising such a component further contains the above-mentioned fatty acid ester of polyglycerin. The content of the fatty acid ester of polyglycerin is usually 0.1 to 3 of the entire flux.
0%, preferably 0.5 to 20%. Since the fatty acid ester of polyglycerin is well mixed with the above-mentioned flux, it does not adversely affect the printability of the cream solder and does not impair the solderability. The cream solder is printed on a printed circuit board through a stencil or the like, on which electronic components are mounted, and then soldered in a hot air oven or the like. After soldering, the flux remains on and around the solder. Since the residue is highly flexible, no crack is generated and at the same time high electrical reliability is provided.

[0011]

【Example】

Examples 1 to 3 and Comparative Examples Next, the present invention will be described with reference to Examples and Comparative Examples.
First, the components shown in Table 1 were mixed and heated to form a uniform solution, and then cooled to form a paste-like flux.

[0012]

[Table 1]

Next, 10 parts of the thus obtained flux and solder powder (Sn / Pb: 63/37, spherical 2
(50-325 mesh) and 90 parts were mixed well to obtain a cream solder. The cream solder was printed on a printed circuit board through a stencil. Next, the printed printed circuit board is preheated at 150 ° C. for 30 seconds, and further,
Heat reflow was performed at 230 ° C. for 45 seconds. The following test was performed to observe the printed circuit board after the reflow, and to further examine the electrical reliability and the properties of the flux residue.

(Insulation Resistance Test) The insulation resistance test was performed according to JIS-Z-3284. That is, the test was performed under the following two conditions. Temperature 40 ± 2 ° C, relative humidity 90-95%, 168 hours Temperature 85 ± 2 ° C, relative humidity 85-90%, 168 hours

(Migration test) JIS-Z-3
284. The temperature and relative humidity were set in an atmosphere under the same conditions as those for the insulation resistance test for 1000 hours.

(Voltage Resistance Test) JIS-Z-31
97.

(Thermal Shock Test) The printed circuit board after reflow was put in air in which the cycle was 125 minutes 30 minutes, exposure 10 minutes, -55 degrees C 30 minutes exposure 10 minutes, and a total of 80 minutes, and 1000 hours later. The residue was observed.

(Pin Contact Cracking Test) After reflow,
After leaving the printed board at room temperature for 24 hours, the flux residue remaining on the surface of the solder on the land was pierced with a needle to determine whether the flux residue had cracks.

(Residue Flexibility Test) A cream solder was printed on a copper plate, preheated under the same conditions, and then reflowed. The flux residue was present on and around the solder, and the flexibility was observed by bending the copper plate at about 90 degrees. Without flexibility, the residue will crack and possibly crack down.

After the cream solder containing the flux shown in Table 1 was reflowed, the above-described test was performed. The test results are shown in Table 2. In the comparative example, migration occurred. Cracks also occurred in the thermal shock test, and cracks occurred in the pin contact test and the flexibility test. However, in the examples of the present invention, cracks and the like were not generated at all, and at the same time, there was no problem with respect to electrical reliability such as an insulation resistance test, a voltage applied humidity resistance test, and a migration test.

[0021]

[Table 2]

[0022]

The cream solder obtained by the present invention has a high electric reliability after reflow and gives a flexible residue, so that it can be used for a flexible substrate or the like. Further, even in an atmosphere in which the temperature changes drastically, there is no generation of cracks in the flux residue, so that the application range is wide.

Claims (2)

[Claims] 1. A soldering flux containing a fatty acid ester of polyglycerin. 2. A cream solder containing the flux according to claim 1 and a solder powder.